Located on the Boise River in southwestern Idaho, the population of Boise at the 2010 Census was 205,671, the 99th largest in the nation. The Boise-Nampa metropolitan area, also known as the Treasure Valley, includes five counties with a combined population of 664,422, the most populous metropolitan area in Idaho. The original Fort Boise was 40 miles (64 km) west, near Parma, down the Boise River near its confluence with the Snake River at the Oregon border.
Set in a high-desert area, the tree-lined valley of the Boise River became a distinct landmark, an oasis dominated by cottonwood trees.
According to the story, a French-speaking guide, overwhelmed by the sight of the verdant river, yelled "" ("The wood! In the 1820s, French Canadian fur trappers set trap lines in the vicinity.
The place where they stood is called Bonneville Point, located on the Oregon Trail east of the city. The name may instead derive from earlier mountain men, who named the river that flows through it.
After trekking for weeks through dry and rough terrain, his exploration party reached an overlook with a view of the Boise River Valley.
About 34 miles (55 km) southwest of Boise, and about 26 miles (42 km) southwest of Nampa, the Owyhee Mountains lie entirely in neighboring Owyhee County.
According to the United States Census Bureau, the city has a total area of 80.05 square miles (207.33 km) according to the United States Census Bureau.
Like all major cities, it is composed of several neighborhoods.
The first capital of the Idaho Territory was Lewiston in north central Idaho, which in 1863 was the largest community, exceeding the populations of Olympia and Seattle, Washington Territory and Portland, Oregon combined. But following the creation of Montana Territory, Boise was made the territorial capital of a much reduced Idaho in a controversial decision which overturned a district court ruling by a one-vote majority in the territorial supreme court along geographic lines in 1866. The downtown area's elevation is 2,704 feet (824 m) above sea level.
Most of the metropolitan area lies on a broad, flat plain, descending to the west.